Sorry I can't tell you what size they are but from some of the pics I have seen of body lifts on this vehicle it doesn't look like they are too big...although they do look bigger than a 15mm.

Speaking of body lifts since you have the bed unbolted you might as well add a couple inches to that baby!

One more thing I forgot to mention which is probably obvious is that you will need to unbolt the filler neck and disconnect any breathers that are routed to the bed.

Finally if the tank has a metal ring which thread over the fuel pump to hold it in (most do) make sure to use a brass punch or wood dowel to unthread it. (don't want to make a spark with a screw driver and blow da hole thing up)

Mike